Where do random contacts disappear to? Even my own kids!?

[nvleisides]

It is so very random to me but certain contacts just disappear.  Contacts I've had for years.  Even my own children....my wife...many others remain the same.  How could anything on my phone disappear through any kind of sync?  Icloud....VZ Contact Transfer?  I don't get it.  In my groups I have my Yahoo and Facebook groups.  I want to get rid of Facebook contacts....too many with only FB contact info.  When I uncheck both groups I have no contacts available.  Don't get it.  Anyone have some leads on this issue?